I am using Susy (with 320Up) and I really like it. -> https://github.com/ericam/320-susy
Basically Susy means that I can have all grids in one.
Even several types of grids depending on resolution due to media queries.
It requires Sass/Compass, so it's not for everyone.
But I am sold.

After reading your first post several times, I went on searching for comparisons and tutorials about less and sass. I finally decided to give sass a chance and now, a few weeks later, I'm really happy with it. Don't want to write plain css ever again. It's so straight forward... Introduced it when I had some already existing css files and changed them whenever I had to touch something - not a problem at all.

Alone the support of variables is something I missed so much all the time...

<strong class="show-on-desktops">You are on a desktop machine.</strong>
<strong class="show-on-tablets">You are on a tablet device.</strong>
<strong class="show-on-phones">You are on a smartphone like an iPhone or Android phone.</strong>

<strong class="hide-on-desktops">You are not on a desktop machine.</strong>
<strong class="hide-on-tablets">You are not on a tablet device.</strong>
<strong class="hide-on-phones">You are not on a smartphone like an iPhone or Android phone.</strong>

That doesn't prevent me from using other frameworks for the front-end - and share the semantic css glue code.
But Bootstrap 2 actually looks like something I could use.
Especially when there's a decent Sass/Compass port.

one of the most convenient features and the thing that got me hooked on Twitter Bootstrap 2 is that its components is all maintained in separate files leaving it highly customizable and easy to choose with components suits your application best.

In my opinion, should we go for Foundation, we could aim for a Yii look.
Instead of - if we chose Bootstrap - looking like one of thousands of other sites built with it.

Mike: Yes, ideally!

Let me suggest the following:

1) Yii goes for ZURB Foundation.
2) Optionally, by means of CSS shims, it could be made to support Bootstrap.
3) If people choose to use Bootstrap, there is an excellent and well-maintained extension by Chris.

Let us choose Foundation because it offers more flexibility and doesn't make Yii generated projects look like yet another Twitter Bootstrap site, but a really cool Yii site.
It wouldn't be a big deal to make it support Bootstrap:

Semantic CSS shim is the answer!

I don't think neither Foundation nor Bootstrap really has semantic CSS built in, but if we create two versions, one for Foundation (the default) and one for Bootstrap (optional), then we can have it all.
Even a third or a fourth CSS framework, like Blueprint.

That solution brings all the power to the users of Yii.

Wrote this in another topic in the Yii 2.0 forum.

Let's not base this on popularity, or what Twitter has chosen to bundle with Bootstrap.

@SapporoGuy
Yup - that's my opinion of Bootstrap as well.
Even though they changed it, I still feel that Foundation - or maybe something else - would be better.
Bootstrap added a lot of sugar, which is why people think it's the coolest thing since sliced bread..

I built an inhouse system and then found bootstrap, i almost cried until i opened up their code and realized that I'm glad a pieces together several different projects and have human readable css. Its not as good but the next person can walkin and within a hour be up and running.

Foundation sites look good my iphone. Bootstrap sites go both ways ... But that is a designers problem probably...

the webapp framework should go with 1140 grid system or its close cousin the
foundation from zurb !
This is to maximize the size of most monitors in used today ... as they both adapt to big screens & small screens alike (mobiles,tablets, handhelds) and on the same token ... they are light !

I will try to integrate one of these 2 css frameworks into my Yii app very soon !